To further improve integration degrees of semiconductors such as of a large scale integration (LSI), finer patterns are made during productions of semiconductors, and currently the smallest pattern size is as small as 45 nm.
The formation of fine patterns in such semiconductor devices can be realized by the exposure technique using electron beams that are capable of forming fine pattern in the size of 100 nm or smaller. The exposure technique using electron beams has a low throughput, and therefore it is not suitable for manufacturing at low cost. Therefore, it has been considered that exposure techniques not using electron beams be developed to shorten wavelength of light from a light source in an exposure device (e.g., Extreme Ultraviolet (EUV) exposure using soft X-rays having a wavelength of 13.5 nm as a light source). However, to shortening light from a light source in the exposure device means to update the exposure device. A considerable cost is expected to carry out this update. Moreover, to form a fine pattern, it is expected that a resist material is developed to have a high resolution corresponding to the light source of the exposure device, but developments of resist materials have limitations and thus it is difficult to provide a resist material having all of the desired characteristics. Therefore, it is desired to take a totally different approach to provide a technology capable of forming a fine resist pattern uniformly and highly accurately without updating exposure devices or developing resist materials.
There is a method called, liquid immersion lithography, as a method for forming a fine resist pattern exceeding exposure limit (resolution limit) of an exposure light source using a conventional exposure device.
The liquid immersion lithography is a method for achieving high resolution by filling a space between a resist and a final projection lens with a liquid having the higher refractive index than that of air. However, resolution of a resist in this liquid immersion is still insufficient, and precise processing for giving a half pitch (hp) of 32 nm, which is regarded as a half pitch of the next generation, cannot be easily performed by the liquid immersion lithography.
Under such circumstances, a double patterning method has recently attracted people's attentions as a technique capable of precision processing to give the 32 nm-half pitch (hp) of the next generation (see, for example, Optical Microlithography XXI, Proc. SPIE, 6924, 6924-8(2008)). This double patterning method is a method to reduce a pitch of the resist pattern by forming a first resist pattern, and forming a second resist pattern in the space formed by the first resist pattern so as to be adjacent to be the first resist pattern. Among the double patterning pattern methods known, the method called Litho Litho Etch (LLE) is particularly advantageous in terms of the cost, and LLE is a method in which a second resist film is developed without etching a first resist film, which has been developed. This LLE is, for example as illustrated in FIGS. 1A to 1D, to form a resist pattern of 100 nm-line (L)/100 nm-space (S) (1:1) (FIG. 1D)), by exposing a first resist film 1 through a certain mask pattern, and developing (FIG. 1A) to form a first resist pattern 2 of 100 nm-line (L)/300 nm-space (S) (1:3) (FIG. 1B); applying a second resist 3 over the first resist pattern 2; and exposing through the same mask pattern sifted from the line pattern of the first resist pattern 2 by 200 nm, and developing (FIG. 1C) to form a second resist pattern 4 as well as exposing the first resist pattern 2 to the air. Since the second resist 3 is applied without dissolving the first resist pattern 2 in this double patterning method, a technique called “resist freezing” that inactivates the first resist pattern 2 in some way is used.
As the resist freezing technique, for example, a technique for applying a short wavelength-ultraviolet rays of 172 nm has been known (see, for example, Advances in Resist Materials and Processing Technology XXV, Proc. SPIE, 6923, 6923-79(2008)). This technique, however, includes a special process which is different from common resist exposure, and thus there are problems that turn around time (TAT) becomes long, practices using the technique is unrealistic, and it is not suitable for productions at low cost.
As another example of the resist freezing technique, a technique using high temperature heating has been known (see, for example, Advances in Resist Materials and Processing Technology XXV, Proc. SPIE, 6923, 6923-16(2008)). This technique, however, can use only the resist material (particularly a resin) that can resist high temperature heating, and therefore it has problems such that variations of the resist materials which can be used are poor, and it is not suitable for productions at low cost.
As yet another example of the resist freezing technique, a technique using a freezing agent containing a crosslinking agent has been known (see, for example, Advances in Resist Materials and Processing Technology XXV, Proc. SPIE, 6923, 6923-17(2008)). This technique, however, causes uneven covering of the resist pattern in the case where there is a difference in densities of the resist pattern, such as in the case of Logic LSI, or different shapes of the resist pattern are present together, and thus there is a problem that it is difficult to form a precise pattern using this technique.
As yet another example of the resist freezing technique, a technique for processing with amine gas has been known (see, for example, J. Photopolym. Sci. Tecnol., 21(5), 655-663(2008)). However, this technique has problems that sensitivity of the resist may decreases, or the residue may be remained as the second resist is poisoned (i.e. resist poisoning) by this process.
As yet another example of the resist freezing technique, a technique using a freezing agent containing a water-soluble resin and a water-soluble crosslinking agent has been known (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2008-83537). However, a coating layer formed by this technique has low transmissiveness against ArF excimer laser light of 193 nm, and thus there is a problem that the first resist pattern is exposed to the air again and dissolves to a developing solution.
As yet another example of the resist freezing technique, a technique using a freezing agent containing a metal compound has been known (see, for example, JP-A No. 2008-33174). However, this technique creates a big difference in etching resistance between the first resist pattern to which the coat layer has been formed and the second resist pattern, and thus there is a problem that it is difficult to secure a process margin.
As mentioned above, the double patterning method using the conventional resist freezing technique has problems that it is difficult to form a precise resist pattern capable of forming a precise pattern at high through put and low cost.
Note that, there has already been disclosed a resist pattern thickening material, which can use ArF excimer laser light for exposure, can thicken a resist pattern without depending on a size of the resist pattern, and can easily and efficiently form a fine pattern and the like using the resist pattern by exceeding the exposure limit (see, for example, JP-A Nos. 2006-259692, 2007-148272, and 2008-107788). However, this material is not expected to be used in the double patterning method.